My '72 has leaked there forever. Tried all kinds of things, new bushings ,various o-rings, etc. and it still drips. I wonder if its casting porosity. Anyway the oil that's dripping is from your primary/trans not from your oil tank. The primary is a separate inventory of oil from your engine. There is some potential for oil transfer between engine and primary but if every thing is in good shape there should be vitrually none.
The oil goes in the oil tank and out on the ground. The trail comes from the primary in the vicinity of the kicker shaft. There is a check ball in the oil pump, right? Maybe it's leaking past there, into the crankcase and the crank bearing into the primary?
Cut to the chase; I don't want to pull the motor and find a welding job.
Your oil tank may be leaking. Only way I know to check is to pull it and leak check. Engine oil goes from the tank to the pump. When the engine starts it unseats the ball check and oil flows thru the engine. If the ball check is leaking by it will collect in the cases and puke out the crankcase vent when you start. A leaking ball check won't give you the symptoms you see.